old bjt amplifier kit

[Antonix]

I have 4 bjt amplifier kit and i want to make some little optimization to improve sound quality and performance with 4ohm load.

Any suggestion on it ?

[Antonix]

The power supply are 50 0 - 50V and the power rated is 100Wrms 8ohm.

[Jan Dupont]

If you want to drive 4 Ohm speakers it would be a very good idea to add at least one extra set of output transistors

[Antonix]

Originally posted by ACD
If you want to drive 4 Ohm speakers it would be a very good idea to add at least one extra set of output transistors

Yes but I can't mount others output transistors.

I want to make make a little optimization to make a little more stable the output and drivers stage.

What do you think about a 100nF capacitor on E - C of Q1
and a 39pF capacatitors on B - C of Q2 and Q3 ?

[djk]

"What do you think about a 100nF capacitor on E - C of Q1 "

I would do 1µF across R7, R8 instead.

I would also use a better opamp, not too fast. A NE5534 with the correct cap would sound much better.

Bypass C4, 5, 7 with 100nF.

I would rather see R10, 11 fed from the stabilized opamp supplies. The values would need to be lowered to keep the current up.

I did a commercial design of a CFP output stage with gain, driven from an opamp, about 10 years ago. It sounded quite good.

[peranders]

Why don't you check out Jan's amp? The same idea but a little bit developed.
http://www.delta-audio.com/PA-34A.htm

[djk]

Not very similar, but I like the Baker clamp with the LEDs.

[ANALOG GUY]

Hi, Antonix do you have sample PCB ?
I have some idea for improve this similar circuit with error phase correction topology.

Regard
analog guy

[edl]

Here is my amp design with OPA frontend. Cheap, simple, but powerful and sounds nice.

schema: http://edl.uw.hu/sch.jpg
parts list: http://edl.uw.hu/parts.jpg